The present invention relates to a method and an apparatus for removing particles from a surface of an article, such as a semiconductor wafer in a clean room, a reactor for coating a surface of a semiconductor device and its peripheral equipment, and a glass for liquid crystal.
A clean room is used to produce semiconductor devices and like, and is required to be free of particles such as dust so as to provide a surface of a semiconductor wafer free of particles. Recently, it has been required, for example, to remove particles from a semiconductor wafer having a dimension as small as several micrometers and preferably particles having a dimension smaller than one micrometer.
A conventional method for cleaning particles from a surface of an article includes a contact process and a non-contact process, as shown in FIG. 8. The contact process includes a fixed brush vacuum process and a rotating brush vacuum process. Both of the contact processes allow the removal of particles having a dimension of not less than scores of micrometers, but does not remove particles having a dimension of up to scores of micrometers.
The non-contact process includes a vacuum process, an air knife process, and a ultrasonic air process. The vacuum process removes particles having a dimension of not less than about 100 micrometers, and the air knife process does not enable the removal of particles having a dimension of not more than scores of micrometers. The ultrasonic air process allows the removal of particles having a dimension as small as several micrometers. However, the ultrasonic air process does not enable the removal of particles having a dimension of not more than 1 micrometer.
The present inventors have proposed removing particles from a wafer by irradiation with an ultraviolet ray, a radiation ray and a laser ray onto a wafer, thereby emitting a photoelectron therefrom so as to remove the particles therefrom (please refer to JP-A-4-239,131 and JP-A-6-296,944). However, a surface of a wafer is directly irradiated by an ultraviolet ray, a laser ray, or a radiation ray in this process. Therefore, if a surface of the wafer is sensitive to these rays, the wafer surface may undergo an unfavorable chemical reaction, thereby limiting its application.
In view of the foregoing, it is an object of the present invention to provide a method and an apparatus for removing particles from a surface of an article, which allows the removal of even particles having a dimension of less than one micrometer.
According to one aspect of the present invention, there is provided a method for removing particles from a surface of an article comprising: supplying the particles with an electric charge; and applying at least one of an ultrasonic wave and a gas stream onto the surface of the article while applying a first electric field for driving away the electrically charged particles from the surface of the article. Electrostatic force driven by the first electric field along with the application of an ultrasonic wave and/or gas facilitates the removal of the particles from the surface.
Preferably, the supplying step comprises bombarding the surface of the article with at least one of electrons and negatively charged ions so as to negatively charge the particles.
The supplying step may comprise the step of irradiating at least one of an ultraviolet ray and a radiation ray onto a photoelectron emitting material in the presence of at least 1 part per million of one of gaseous oxygen and water so as to produce a negatively charged ion. The supplying step may further comprise the step of applying a second electric field for driving the negatively charged ion in a direction toward the surface of the article, whereby the negatively charged ion interacts with the particles so as to supply them with an electric charge. Alternatively, convection generated by the irradiation of the ultraviolet ray carries the negatively charged ions to the particles on the surface of the article.
Preferably, the supplying step comprises the step of conducting electric discharge to produce a negatively charged ion.
Preferably, the supplying step may further comprise the step of applying a second electric field for driving the negatively charged ion in a direction toward the surface of the article, whereby the negatively charged ion interacts with the particles so as to supply the particles with an electric charge. Alternatively, convection generated by the irradiation of the ultraviolet ray carries the negatively charged ions to the particles on the surface of the article.
Preferably, the method further comprises the step of collecting the particles removed from the surface. The collecting step may comprise the step of supplying the particles removed from the surface with at least one of electrons and negatively charged ions. The collecting step may comprise the steps of: irradiating at least one of an ultraviolet ray and a radiation ray onto the photoelectron emitting material in the presence of at least 1 part per million of one of gaseous oxygen and water so as to produce a negatively charged ion; and applying a second electric field for driving the negatively charged ion in a direction toward the surface of the article. Alternatively, the collecting step may comprise the step of conducting electric discharge to produce a negatively charged ion.
Preferably, particles having a dimension of not more than 5 micrometers are removed from the surface of the article. Further preferably, particles having a dimension of not more than 1 micrometer are removed from the surface of the article. Preferably, the particles have a dimension of at least 0.1 micrometer.
Preferably, the article comprises a semiconductor wafer being disposed above a first electrode. Preferably, the article comprises a semiconductor wafer standing and being close to a first electrode.
Preferably, the first electric field ranges from 10 volts to 100 kilovolts per centimeter. Preferably, the second electric field ranges from 0.1 volts to 2 kilovolts per centimeter. Preferably, the second electric field ranges from 10 volt to 1 kilovolts per centimeter.
According to another aspect of the present invention, there is provided an apparatus for removing a particle from a surface of an article comprising: an ionizing device for supplying particles on a surface of an article with an electric charge; at least one of an ultrasonic generator for applying an ultrasonic wave to a surface of an article and a stream source for generating a gas stream onto a surface of an article; and a first electrode for forming an electric field for driving electrically charged particles from a surface of an article.
Preferably, the ultrasonic generator comprises at least one of a piezoelectric oscillator, a polymer piezoelectric membrane, an electrostrictive oscillator, a Langevin oscillator, a magnetostrictive oscillator, an electrodynamic transformer, and a capacitor transformer. Further preferably, the ultrasonic generator comprises a piezoelectric oscillator.
Preferably, the stream source comprises an air knife.
Preferably, the ionizing device comprises a photoelectron emitting material and a light source for irradiating at least one of an ultraviolet ray and a radiation ray onto the photoelectron emitting material.
Preferably, the ionizing device is capable of conducting electric discharge. Preferably, the ionizing device comprises a pair of second electrodes wherein electricity passes through a gas between the second electrodes. Preferably, the ionizing device comprises a heater for generating convection.
Preferably, an apparatus further comprises a trap for collecting a particle removed from an article. The trap may comprise a third electrode for trapping particles removed from an article.